I'm sorry but either learn how to deal with these situations or get out of the game. Complaining after the fact on the internet is not going to help you.
It sounds like the person who hired you told you not to use flash. You will get people who don't want it cause it's distracting, and you'll have to know to address it in contract or work around situations like that. If it was cause they thought they knew more about photography than you, you need to find better ways to communicate with the client.
If it wasn't the client, you need to find ways to deal with whatever the situation is that you want to be vague about, cause no one here can read your mind or help you if they don't know what the situation is.